Questions about KMS flip

[Christian König]

Am 16.11.21 um 09:00 schrieb Lang Yu:
> On Tue, Nov 16, 2021 at 08:14:08AM +0100, Christian KKKnig wrote:
>> Am 16.11.21 um 04:27 schrieb Lang Yu:
>>> On Mon, Nov 15, 2021 at 01:04:15PM +0100, Michel DDDnzer wrote:
>>>> [SNIP]
>>>>> Though a single call to dce_v*_0_crtc_do_set_base() will
>>>>> only pin the BO, I found it will be unpinned in next call to
>>>>> dce_v*_0_crtc_do_set_base().
>>>> Yeah, that's the normal case when the new BO is different from the old one.
>>>>
>>>> To catch the case I described, try something like
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c b/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c
>>>>
>>>> index 18a7b3bd633b..5726bd87a355 100644
>>>>
>>>> --- a/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c
>>>>
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c
>>>>
>>>> @@ -1926,6 +1926,7 @@ static int dce_v11_0_crtc_do_set_base(struct drm_crtc *crtc,
>>>>
>>>>                   return r;
>>>>
>>>>
>>>>
>>>>           if (!atomic) {
>>>>
>>>> +               WARN_ON_ONCE(target_fb == fb);
>>>>
>>>>                   r = amdgpu_bo_pin(abo, AMDGPU_GEM_DOMAIN_VRAM);
>>>>
>>>>                   if (unlikely(r != 0)) {
>>>>
>>>>                           amdgpu_bo_unreserve(abo);
>>>>
>>> I did some tests, the warning can be triggered.
>>>
>>> pin/unpin operations in *_crtc_do_set_base() and
>>> amdgpu_display_crtc_page_flip_target() are mixed.
>> Ok sounds like we narrowed down the root cause pretty well.
>>
>> Question is now how can we fix this? Just not pin the BO when target_fb ==
>> fb?
> That worked. I did a few simple tests and didn't observe ttm_bo_release warnings
> any more.
>
> The pin/unpin logic,
>
> 1, fist crtc_mode_set, dce_v*_0_crtc_do_set_base() pins crtc->primary->fb(new),
> old_fb is NULL.
>
> 2, second crtc_mode_set, dce_v*_0_crtc_do_set_base() pins crtc->primary->fb(new),
> unpins old fb.
>
> 3, amdgpu_display_crtc_page_flip_target() pin/unpin operations.
>
> 4, third crtc_mode_set, dce_v*_0_crtc_do_set_base() pins crtc->primary->fb(new),
> unpins old fb (it is pinned in last call to amdgpu_display_crtc_page_flip_target)
>
> 5, amdgpu_display_crtc_page_flip_target() pin/unpin operations.
>
> .....
>
> x, reboot, amdgpu_display_suspend_helper() is called, the last pinned fb was unpinned.
>
> And I didn't observe amdgpu_bo_unpin() in dce_v*_0_crtc_disable() is called.
>
> If the logic is wrong, please correct me.

I can't fully judge because I'm not that deep with my head in the old 
display code, but from a ten mile high view it sounds sane to me. Michel 
what do you think?

BTW: Nicholas are there any plans to get rid of all that stuff? It would 
be a really nice cleanup of rather flaky code I think.

Thanks,
Christian.

>
> Regards,
> Lang
>
>> Thanks,
>> Christian.
>>
>>> Regards,
>>> Lang
>>>